1. Field of Invention
The invention concerns the production of three-dimensional bodies (3D-bodies) using layer build-up processes (powder based generative rapid prototyping processes), and in particular the production of suitable powder layers, as well as the production of 3D-bodies from these powder layers, wherein in particular layered powder material is employed.
3D binder printing is among the newer and particularly interesting powder based generative rapid prototyping processes.
2. Related Art of the Invention
In a first variation of 3D binder printing a layer of powder material or granulates is applied upon a substrate, after which predetermined areas, which respectively correspond to a layer of an object to be produced, are moistened with a liquid binder. The powder particles are cross-linked or adhered in the moistened areas by the liquid binder. Upon the subsequent evaporation of the solvent in the liquid binder, the powder particles adhere directly to each other, wherein they are coalesced with each other at least in their edge areas. 3D-binder printing processes, which are particularly directed to this type, are know for example from European Patents EP 0644 809 B1, EP 0686 067 B1 and European Patent Application EP 1 099 534 A2.
From EP 0 925 169 B1 a further variant of the 3D binder printing process is known, in which mixtures of powders, fillers and adhesives are employed. The binder liquid basically comprises essentially only a solvent for the adhesive contained in the mixture. In this embodiment, the adhesive can also be present in the form of a surface coating of the powder particles. Therein, it is known to use water soluble polymers as the powder particle surface coating, and aqueous binder liquids. Water soluble systems have however the disadvantage, that they tend to agglomerate or adhere upon exposure to ambient humidity.
DE 198 13 742 C1 discloses a process for production of three dimensional objects by sequential layer buildup involving hardening with electromagnetic radiation powder particles solidifiable by exposure to electromagnetic radiation. A device is proposed for reducing charge differences of the layer-forming powder particles in the dispensing device, in order to prevent the powder particles from plugging up the outlet aperture.
The known processes have the disadvantage, that the powder particles frequently agglomerate during dispensing from the dispensing device and during layering on the substrate. In general, there is found on the layer, besides the primary powder particles, also more or less large agglomerates, which lead to uneven powder layers and defects in the bodies formed therefrom. Agglomerates in particular interfere when using a smoothing device for the applied powder layer.
For the production of homogenous bodies with consistent quality the powder must be agglomerate-free, essentially from the time of leaving the dispensing device. Also, the electrostatic charging of the powder particles by rubbing against each other while leaving the dispensing device must be avoided.